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I'm sure you know that Quakers practiced complete pacifism, so of course no one could have fought in a war and been a Quaker... Plus, The United Brethern church was established sometime in the mid 1700s, in Lancaster Pa, by German speaking emigrants, and was an offshoot of the Mennonite/German Reform churches..so, this would be in keeping with Isaac's German heritage, If looking for the families in Pa, I'd think seeking out Mennonite/German Reform, and even Lutheran records might stand a chance of finding them.
As you know Henry's date of death, and place, have you checked to see if there is an obit for him in a newspaper where he lived? The Ohio Historical Society, in Columbus, has a huge library of filmed Ohio newspapers that are available through interlibrary loan, so you might visit their online site and go through the list of what they have available.
Was Henry married to a Lydia Kleinfelder? If so I found him in a book about York Co, Pa families...lydia, b 1824 m Henry on 11-7-1841. It goes on to say he died in 1844, so this looks like it could be your Henry. If so, Lydia was dau of Jacob and Catharine Lutz Kleinfelder... they had their children in Chanceford, York Co, Pa, but moved to Marion Co, Ohio, where Jacob died March 1m 1840.